Disappearing Mulches

09/01/2010 02:00:00 AM

By Renee Stern
Contributing Editor

Growers rely on plastic mulches to control weeds, warm soil and improve crop quality, but disposal costs and other issues have produced keen interest in biodegradable alternatives.

Some products already on the market include paper and compostable cornstarch-and-biodegradable polymer blends. Cost and longevity remain grower concerns, however.

By reducing herbicide applications and trips through the field, “Compostable [mulch] is a huge step in the right direction,” says Tom Thornton, co-owner of Cloud Mountain Farm & Nursery in Everson, Wash.

But, he says, “If we have to put in the labor to pull it up at the end of the season, whether to take it to a landfill or a compost facility, that’s unacceptable.”

Thornton serves on the advisory board for a new multistate research project on biodegradable mulches and high-tunnel production systems. He’s eager to find cost-effective ways for his own operation to control weeds without herbicides.

Project researchers in Washington, Texas and Tennessee are comparing two cornstarch-based mulches and an experimental polylactic acid-based material designed to biodegrade. The trials use two control mulches: the standard black plastic and a biodegradable paper mulch.

Other researchers are pursuing a biodegradable plastic, including Michael Orzolek, professor of vegetable crops at Penn State University in University Park, and Mathieu Ngouajio, associate professor of horticulture at Michigan State University in East Lansing.

Economics and materials sciences, too

The combined mulch and high-tunnel research, now ending its first growing season, tackles not only horticultural aspects but also taps experts in economics and materials sciences. Project director Debra Inglis, a Washington State University professor and Extension plant pathologist at the university’s Mount Vernon Research Center, says growers want to adopt sustainable practices, such as replacing plastics with renewable materials.

The trials in Mount Vernon; Lubbock, Texas; and Knoxville, Tenn., will test differences in crop yield and quality and in mulch degradation in widely different growing conditions, Inglis says. As a plant pathologist, she’ll be checking for any signs of root or foliar disease variations.

The mulch tests use plots planted with tomatoes.

Doug Hayes, professor of chemical and biosystems engineering at the University of Tennessee in Knoxville, leads the project’s work on a new spun-bonded nonwoven film of polylactic acid. Tiny but strong fibers create a flexible material that should hold up through the growing season, Hayes says.

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